Question

The reactivity ratios of monomer 1 and monomer 2 are r₁ and r₂. If r₁ = r₂ = 0

• A. Alternating copolymer will form
• B. Block copolymer will form
• C. Random copolymer will form
• D. Homopolymer will form

Hint:

Zero reactivity ratios are a hallmark of perfectly alternating copolymerization.

Answer 1

The Correct Option is A

Step 1: Understanding reactivity ratios.
Reactivity ratios indicate the preference of a growing polymer radical to add the same or a different monomer. They play a crucial role in determining the copolymer microstructure.
Step 2: Meaning of r₁ = r₂ = 0.
When both reactivity ratios are zero, a radical of monomer 1 cannot add monomer 1, and a radical of monomer 2 cannot add monomer 2. Each radical can only add the opposite monomer.
Step 3: Analysis of options.
(A) Alternating copolymer will form: Correct — Strict alternation of monomers occurs.
(B) Block copolymer will form: Requires sequential polymerization, not governed by r values.
(C) Random copolymer will form: Occurs when r₁ and r₂ are close to 1.
(D) Homopolymer will form: Requires r values much greater than 1.
Step 4: Conclusion.
If r₁ = r₂ = 0, an alternating copolymer is formed, making option (A) correct.

Answer 2

Rather than recalling what each r-value regime is "called," we can directly build up the polymer chain sequence implied by r₁ = r₂ = 0 and see what structure falls out.

1. Alternating copolymer: Since r₁ = 0, a radical ending in monomer 1 has zero probability of adding another monomer 1 and must add monomer 2. Likewise, since r₂ = 0, a radical ending in monomer 2 must add monomer 1. Following the chain step by step: 1 forces the next unit to be 2, and 2 forces the next unit to be 1, giving the forced sequence ...-1-2-1-2-1-2-... This strict, forced alternation is precisely the definition of an alternating copolymer, matching the built-up sequence exactly.
2. Block copolymer: A block structure (long runs of monomer 1 followed by long runs of monomer 2) would require a radical of monomer 1 to keep adding more monomer 1 for a while, which needs r₁ to be large, not zero - the opposite of the given condition.
3. Random copolymer: A random sequence would require both types of addition (self and cross) to be roughly equally likely, i.e. r₁ and r₂ both close to 1, not zero.
4. Homopolymer: A homopolymer sequence would need one radical type to almost exclusively keep adding its own monomer, i.e. one r value being very large; with both r values at zero, self-addition is completely forbidden for both monomers, ruling this out entirely.

Directly tracing the forced addition sequence when both reactivity ratios are zero produces a strictly alternating chain.

Therefore, the correct answer is Alternating copolymer will form.